Matrix-type electrodes having braze-penetration barrier

ABSTRACT

A braze-penetration barrier is provided for a sintered and infiltrated matrix-type of electrode or contact, so that, in effect, two joints are provided, one joint being provided between the metallic braze-penetration barrier and the sintered and infiltrated body portion of the matrix-type contact or electrode, and the other or second joint being provided between the metallic braze-penetration barrier member and the supporting rod-like metallic stem-portion of the interrupting contact or electrode. The braze-penetration barrier member may be provided, for example, by pressing a preformed braze-penetration barrier member with the particles of the matrix system in the press, which is subsequently sintered and infiltrated with a lower-meltingtemperature infiltrant material, such as copper or silver, for example, which penetrates into the pores of the higher-meltingtemperature matrix material, such as tungsten or chromium, for example.

Wayland ttes tent 1 MATRIX-TYPE ELECTRODES HAVING BRAZE-PENETRATIONBARRIER [75] Inventor: Paul O. Wayland, Montour Falls,

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Sept. 25, 1972 [21] Appl. No.: 292,210

[52] US. Cl. 29/630 C, 29/420, 29/630 R, 200/166 C, 200/166 CM [51] Int.Cl. H01b 19/00 [58] Field of Search..... 200/166 C, 166 CM, 166 F;29/630 C, 630 R, 420, 420.5

[56] References Cited UNITED STATES PATENTS 2,389,061 11/1945 Kuzmick29/420 2,706,759 4/1955 Williamson 200/166 C 3,152,892 10/1964 Clark 1.29/420 3,226,517 12/1965 Schreiner 29/630 C 3,359,623 12/1967 Gwyn, Jr29/420.5

3,514,559 5/1970 Ranheim 200/166 C 3,592,987 7/1971 Lempert 200/166 C3,615,901 10/1971 Medicus 29/420.5 3,627,963 12/1971 Lindsay ZOO/166 CPrimary ExaminerCharles W. Lanham Assistant ExaminerJames R. DuzanAttorney, Agent, or FirmW. R. Crout 5 7] ABSTRACT The braze-penetrationbarrier member may be provided, for example, by pressing a preformedbraze-penetration barrier member with the particles of the matrix systemin the press, which is subsequently sintered and infiltrated with alower-melting-temperature infiltrant material, such as copper or silver,for example, which penetrates into the pores of thehigher-melting-temperature matrix material, such as tungsten orchromium, for example.

5 Claims, 8 Drawing Figures REFERENCES TO RELATED APPLICATIONS Applicantis not aware of any related patent application pertinent to the instantinvention.

BACKGROUND OF THE INVENTION Typical construction practice for attachingthe contacts of a vacuum interrupter to the terminal electrodes is bybrazing with high-temperature materials (i.e., those which melt above800C). A particular problem, which is encountered when this joint ismade against sintered and infiltrated matrix-type contacts orelectrodes, such as, for example, chromium infiltrated with copper, isthe following. Since the matrix is never much more than 98 percenttheoretical density, it, therefore, has interspersed micropores. Thesemicropores are available to highly-wettable braze fillers, such ascopper-nickel-manganese alloys, and are dragged away from the jointregion in an unpredictable manner, thus creating unsound joints.Alternative braze fillers, such as copper-gold alloys, do not exhibitthis tendency, but are expensive relative to copper-nickelmanganesealloys.

Accordingly, the present invention is concerned with joiningcircuit-interrupting contacts or electrodes to supporting rod-like stemportions in a manner which is conductive to a sound joint therebetween,and which is capable of resisting shock forces during the opening andclosing operations of the circuit interrupter without breaking thecontact head body portion away from its rod-like supporting stemportion.

SUMMARY OF THE INVENTION The present invention solves the foregoingproblem by associating a thin metallic braze-penetration barrier withthe fabrication of the sintered and infiltrated matrix-type head portionof the contact. In one process, for example, the braze-penetration thinmetallic barrier member constitutes an insert, which is utilized in thepressing operation to press the powdered hightemperature materials priorto the subsequent sintering operation. Following the subsequent infusionof the infiltrant material, such as copper, or silver, for example, intothe micropores of the sintered matrix-type contact, the thin metallicbraze-penetration barrier member is firmly joined to the head portion ofthe matrix-type contact. As a second operation, the metallic supportingstem portion is joined, such as by a separate brazing process, to theaforesaid relatively thin metallic insert member constituting abraze-penetration barrier member. The braze-penetration barrier membermay be, for example, a preformed thin metallic member formed, forexample, of mild steel, with a cup-like depression, and associated withthe pressing and sintering operations. As mentioned, there then resultsthe second sound joint between the outer exposed surface of the thinmetallic braze-penetration barrier member and the associated supportingrod-like stem portion of the final contact assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional viewtaken through a vacuum-type circuit interrupter illustrating theprinciples of the present invention, the contact structure beingillustrated in the closed-circuit position;

FIG. 2 is a fragmentary enlarged detailed view of the lower movablecontact of the interrupting device of FIG. 1 illustrating the improvedmetallic brazepenetration barrier member of the present invention joinedby brazing to the supporting-stem portion;

FIG. 3 is a plan view taken of the movable contact, the view being takensubstantially along the line IIIIII of FIG. 1;

FIG. 4 diagrammatically illustrates the pressing operation in aconventional-type press, wherein the thin metallic braze-penetrationbarrier member is pressed, as

an insert, along with the powdered granular material 'of the refractorymatrix body;

FIG. 5 illustrates the green compressed compact which is removed fromthe press and later subjected to a sintering operation;

FIG. 6 illustrates the infiltration process, wherein a relativelylow-temperature infiltrant material, such as copper, or silver, isplaced upon the sintered matrix body for subsequent infiltration;

FIG. 7 illustrates the finished infiltrated blank piece aftervacuum-melting and prior to the machining operations; and

FIG. 8 is a vertical sectional view taken through the machined finishedcontact head illustrating more clearly the thin metallic cup-shapedbraze-penetration member.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 generally illustrates avacuum-type circuit interrupter, generally designated by the referencenumeral l, and illustrated in the closed-circuit position. As shown, thevacuum bottle or interrupter 1 comprises an upper end plate 2, aninsulating wall envelope 3, formed of a suitable ceramic material, forexample, and a lower end plate 4. A stationary contact structure,generally designated by the reference numeral 5, projects interiorlywithin the upper end plate 2, and includes a supporting electroderod-like stem-portion 6, which is joined by a brazing operation, as morefully described hereinafter, to a stationary contact 7, the latter beingmachined to a configuration more clearly shown in FIGS. 2, 3 and 8 ofthe drawings.

Cooperable with the stationary contact 7 is a lower movable contact 10,joined by a similar brazing operation to an upwardly-extending rod-likesupporting stem-portion 12, the latter extending through a metallicbellows seal 14, as well known by those skilled in the art. In moredetail, the lower end of the metallic bellows seal 14 is brazed withinan aperture 16, provided in the lower end plate 4, whereas the upper endof the bellows 14 is suitably secured to the stem-portion 18 of themovable contact assembly, generally designated by the reference numeral20.

During the opening operation, the movable contact 10 is moved downwardlyby a suitable operating means, not shown, and disengages from thestationary contact 7 to establish an arc therebetween (not shown). Thisarc is rotated around the separated contacts by the magnetic forcesgenerated, and due to the evacuated condition within the envelope 3,this are is quickly extinguished. To prevent the deposition of metallicvapor along the inner walls 30 of the ceramic casing 3, there isinterposed between the arcing region 8 and the ceramic envelope 3 ametallic condensing shield, designated by the reference numeral 24.Generally, the manner of arcing is set forth in US. Pat. No. 2,949,520Schneider, and the method of preventing the deposition of the metallicvapor on the inner walls 3a of the envelope 3 is set forth in US. Pat.No. 2,892,911 Crouch.

The present invention is not concerned with the details of interruption,but is directed specifically to the fabrication of either the stationarycontact assembly 13, or the movable contact assembly 20 by the joining,or brazing operations of the electrode stem-portions 6 or 12 to theassociated stationary and movable contacts 7 or 10 by the manipulatingmeans described more fully hereinafter.

In the fabrication of powder metal components which are made by pressingthe higher-temperature component of the system into a porous matrix, andthen sintering and subsequently infusing a lower-melting-temperaturematerial into the pores, it is usually the case that a theoreticaldensity of perhaps 97 to 99 percent results. This means that some of thepores in the matrix (1 to 3 percent) are unfilled. Many applications forinfiltrated matrix parts, such as electrical contacts, require brazingto some other material, such as a copper conductor supporting stem, withhighly wettable braze materials, such as copper-nickelmanganese alloys,or high-temperature gold alloys.

In practice, I have discovered that some fraction of these brazingsolders will penetrate the l to 3 percent voids in the powder metalpart, thereby making it impossible to accurately predict the properamount of braze material to be placed into the joint. Since the amountof braze material, normally required for such a joint, is very small incomparison to the masses of the parts to be joined, and it was notuncommon to have excess braze material, which would run out of the joint(as with a 1 percent voided contact), or a deficiency of braze materialleaving a weak joint, in the case where we were brazing to a contactwith 3 percent voids, i.e., the variation ranging from 1 to 3 percentvoids may represent a volume for possible takeup of the brazingmaterial, which is nearly equivalent to the volume of braze materialrequired to make an adequate joint.

My present invention is particularly related to a method and contactarticle, and, in part, concerns the making of a powdered metal part froma porous metal matrix infiltrated with a lower-temperature infiltrantmaterial, such as copper or silver, for example, in which isincorporated a dense metallic layer to act as a braze barrier againstbraze material being taken into the l to 3 percent voids, which areusually present in the infiltrated matrix body. In my invention, in oneexample, press a refractory powder together with a mild steel insert,for example, to a controlled porosity level, and then sinter andsubsequently infiltrate with the lower-temperature infiltrant, such ascopper or silver, for example. After infiltration, the insert isintimately attached, or joined to the matrix body via the infiltrantmaterial. The mild steel insert, for example, acts as a braze barrieragainst braze material penetrating the residual voids, or micropores ofthe infiltrated matrix body, thus permitting placement of just exactlythe proper amount of braze material to form a sound mechanical andelectrical joint. The joint is then a composite joint between theinfiltrated matrix body joined to the steel insert via the infiltrantmaterial, and then from the steel insert to the rod-like supportingmaterial, or conductor stem via a highly predictable volume ofhigh-temperature braze material.

In general, the constraints, or limits, on the materials usable in sucha system are is follows: The matrix can be any powdered metal, metaloxide, or semiconducting material. The infiltrant must be of a lowermelting point than the matrix, and the insert, or braze barrier piece,or member must be of a higher-melting point than the infiltrant, andmust be non-reactive with the matrix and infiltrant to an extent, whichexcludes it from being destroyed during the sintering and infiltrationprocesses.

Typical materials for the system are the refractories chromium,molybdenum and tungsten for the matrix material, for example, copper orsilver, for example, for the infiltrant, and mild or stainless steel,nickel or refractories, for example, for the braze-penetration barriermember.

The composition of a particularly desirable matrixlike contact, suitablefor the contact body portion 10, is set forth in British Patent No.1,194,674 by Alfred Alexander Robinson, published June 10, 1970, andassigned to the English Electric Company of England. Also, CanadianPatent No. 836,115 relates to the same composition, and the details offabrication of the matrix-like contact body are set forth in detail inthese two patents.

For reference, the melting points and boiling points of metals, hereinreferred to, are given by certain authorities as follows in degreescentigrade:

Melting Point Boiling Point silver (Ag) 960.8 2200 copper (Cu) 1083 2570cobalt (Co) 1492 3000 chromium (Cr) 1800 2665 molybdenum (Mo) 2625 4800tungsten (W) 3380 6000 FIGS. 4-8, generally, illustrate one process forfirmly attaching the braze penetration insert member 30 to therefractory matrix material 31 in a hydraulic press 32. The plunger 33moves downwardly within the hydraulic press, compacting the matrixmaterial, and following ejection from the press 32, as pictured in FIG.5, the piece is then sintered and subsequently infiltrated with asuitable infiltrant material, such as copper, or silver 35, for example,as illustrated in FIG. 6.

Many braze materials are available in the improved process of myinvention. For example, I have obtained good results with No. l600-Nbrazing alloy, sold by Coast Metals, Inc. of Little Ferry, New Jersey,having a nominal composition of copper 52.5 percent, manganese 38.5percent, and nickel 9 percent by weight. Another alternate brazingmaterial may be Handy and Harman of New York City, with their Handy HighTemp 095 brazing material having a nominal composition of copper 52.5percent, nickel 9.5 percent, with the balance manganese, with boronmaximum 0.10 percent, iron maximum content of 0.10 percent, and totalother impurities maximum content 0.50 percent. The Handy High Temp 095is a relatively ductile copper-manganese-nickel brazing alloy forjoining iron base and nickel base heat-resistant alloys.

From the foregoing, it will be noted that there is provided thebraze-penetration barrier, which prevents the penetration of the brazingmaterials into the micropores of the contact head body. As a result, apredetermined amount of brazing material may be used, and joints may bepredictably sound in nature.

Although I have illustrated the utilization of a brazing insert 30 inthe hydraulic pressing operations, as set forth in FIGS. 5-7 of thedrawings, it will be obvious to those skilled in the art that other waysof attaching the braze penetration member 30 to the matrix contact orelectrode body 31 will be evident.

As will be recognized by those skilled in the art, the invention isapplicable also to fixed electrodes in triggered gap-type devices havingtwo spaced fixed electrodes therein.

Although I have illustrated and described a particular article andprocess, and means for making a contact assembly, it is to be clearlyunderstood that the same were merely for the purpose of illustration,and that changes and modifications may readily be made therein by thoseskilled in the art, without departing from the spirit and scope of theinvention.

What is claimed is:

l. The method of fabricating an impregnated refractory contact structurefor a circuit-breaker, comprising the sequential steps of:

a. placing a metallic plate-like barrier insert (30) within a mold;

b. placing a predetermined quantity of metallic powdered matrixrefractory pulverulent material only within the mold against saidplate-like barrier insert;

c. cold-pressing the refractory pulverulent material with the insert toresult in a green" contact member;

d. removing the green contact member from the mold and sintering thesame to remove gas therefrom;

e. infusing the sintered powdered body with a metallic infiltrantselected from the group consisting of copper, silver and their alloys;whereby the insert is firmly bonded to the matrix body of the contact;and,

f. metal-joining a metallic supporting stem portion to said contact.

2. The method of claim 1, wherein the refractory pulverulent material isselected from the group consisting of tungsten, chromium, molybdenum andtheir alloys.

3. The method of fabricating an impregnated refractory contact structurefor a circuit-breaker, comprising the sequential steps of:

a. preforming a metallic plate-like barrier member into a cup-shapedinsert;

b. placing said cup-shaped insert within a mold;

c. placing a predetermined quantity of metallic powdered matrixrefractory pulverulent material only within the mold against saidcup-shaped barrier in sert;

d. cold-pressing the refractory pulverulent material with the cup-shapedinsert to result in a green contact member;

e. removing the green contact member from the mold and subsequentlysintering the same to remove gas therefrom;

f. infusing the sintered powdered body with a metallic infiltrantselected from the group consisting of copper, silver and their alloys;whereby the cup-shaped insert is firmly bonded to the matrix body of thecontact; and,

g. metal-joining a metallic supporting stem portion to said cup-shapedinsert and thus to the contact body.

4. The combination according to claim 3, wherein the refractory materialis selected from the group consisting of tungsten, molybdenum andchromium and their alloys.

5. The method of claim 4, wherein the cup-shaped insert is selected fromthe group consisting of mild steel and stainless steel.

2. The method of claim 1, wherein the refractory pulverulent material isselected from the group consisting of tungsten, chromium, molybdenum andtheir alloys.
 3. The method of fabricating an impregnated refractorycontact structure for a circuit-breaker, comprising the sequential stepsof: a. preforming a metallic plate-like barrier member into a cup-shapedinsert; b. placing said cup-shaped insert within a mold; c. placing apredetermined quantity of metallic powdered matrix refractorypulverulent material only within the mold against said cup-shapedbarrier insert; d. cold-pressing the refractory pulverulent materialwith the cup-shaped insert to result in a ''''green'''' contact member;e. removing the ''''green'''' contact member from the mold andsubsequently sintering the same to remove gas therefrom; f. infusing thesintered powdered body with a metallic infiltrant selected from thegroup consisting of copper, silver and their alloys; whereby thecup-shaped insert is firmly bonded to the matrix body of the contact;and, g. metal-joining a metallic supporting stem portion to saidcup-shaped insert and thus to the contact body.
 4. The combinationaccording to claim 3, wherein the refractory material is selected fromthe group consisting of tungsten, molybdenum and chromium and theiralloys.
 5. The method of claim 4, wherein the cup-shaped insert isselected from the group consisting of mild steel and stainless steel.